<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<ul>
    <li>aaa</li>
    <li>bbb</li>
    <li>ccc</li>
</ul>
<script>
    var s = '';
    s = s + '<li>aaa</li>';
    s = s + '<li>bbb</li>';
    s = s + '<li>bbb</li>';
    console.log(s);
    //+=
    var s2 = ''
    s2 += '<li>aaa</li>';
    s2 += '<li>bbb</li>';
    s2 += '<li>ccc</li>';
    console.log(s2);

    var a = 1;
    a += 2;  //a = a + 2
    a += 3;  //a = a + 2
    console.log(a);

    a -= 2; //a = a -2
    console.log(a);

    a *= 3; //a = a * 3;
    console.log(a);

    a /=2;   //a = a / 2
    console.log(a);


</script>
</body>
</html>